Author: Kuan Ling Chen, Jiajin Fan, Maduka M. Kaluarachchi, Wei Nie 👨🔬
Affiliation: Inova Schar Cancer Institute 🌍
Purpose: This study evaluates the impact of CBCT acquisition speed on the accuracy of moving target alignment during image-guided radiotherapy. Additionally, the influence of target motion speed and range was assessed to determine optimal imaging parameters for motion management.
Methods: Averaged 4DCT (AVE) scans were generated from 4DCT scans of a motion phantom that moved in ranges of 0.5, 1, 2 and 3cm at breathing rates of 10 and 20bpm. Gross tumor volumes (GTVs) were contoured on all 10 respiratory phases and combined to form internal GTV (iGTVs), which were then transferred to each AVE scan as planning targets. CBCT images of the motion phantom were acquired on a Ethos system with fast (~6s) and slow (~60s) acquisition modes. Additional scans with similar parameters were performed on a TrueBeam for comparison. Targets were re-contoured on each CBCT and the target alignment were evaluated based on variations in motion range, respiratory rate and acquisition speed.
Results: The results indicate that target locations on slow scans from Ethos and TrueBeam closely align with those on the AVE scans, offering consistency in motion management. However, target location on Ethos fast scans showed variability depending on the acquisition start time relative to the breathing phase (e.g. valley vs peak). The target volumes seen on fast scans may vary depending on the breathing rate. At lower breathing rate, the deviation of target volumes on fast scans from those seen on the AVE scans is more pronounced. This variability highlights the challenges of fast acquisition for accurate target localization in patients with significant motion ranges.
Conclusion: For treating moving targets, slow CBCT technique on Ethos provides superior target alignment, especially for patients with lower respiratory rates and larger motion ranges. These findings emphasize the importance of using appropriate imaging protocols to enhance accuracy in moving targets.